The ability to form a material surface possessing self-cleaning characteristics, i.e., capable of repelling contamination, has been a major goal for many years in many fields of study including fiber/textile technologies as well as technologies dealing with countless other types of organic as well as inorganic surfaces. Primarily, research in this area has been directed to methods for forming materials possessing surfaces that display very limited wettability, which can help to provide a self-cleaning surface to a substrate.
As with many other questions in many other fields, nature has already developed an efficient solution to this problem. First dubbed the “lotus effect” and described by Dr. Wilhelm Barthlott of the University of Bonn (see, for example, “Purity of the sacred lotus, or escape from contamination in biological surfaces,” Planta (1997) 202:1-8.), the external surfaces of many plants and animals have a rough surface structure combined with an ideal surface chemistry to create self-cleaning, super-repellant surfaces. For example, the self-cleaning characteristics found on the leaf surface of the N. nucifera (the white lotus) and the wing surface of many insects combine a topology describing a high degree of surface roughness with a chemistry that exhibits low surface energy to create a surface upon which practically all particulates are removed when subjected to water, e.g., rain, independent of the size and chemical nature of the particles.
Attempts have been made to replicate the lotus effect on various surfaces. For example, Youngblood, et al. prepared ultrahydrophobic polypropylene surfaces by simultaneously etching the polypropylene and sputtering poly(tetrafluoroethylene) using inductively coupled radio frequency argon plasmas (Macromolecules 1999, 32, 6800-6806). Another group, Kim and Kim of UCLA, have utilized lithographic techniques to create ultrahydrophobic silicon-based surfaces including nano-sized channel configurations formed on the surfaces (IEEE MEMS 2002, 479-482). While such methods have shown capability for creating a rough surface on particular materials, the methods are fairly limited in application and also require expensive and complicated processing techniques.
What is needed in the art are improved surface modification techniques applicable to a wide variety of materials so as to provide ultrahydrophobic, e.g., self-cleaning, surface characteristics to materials and products.